This invention relates to the manufacture of optical fibre, particularly high quality optical fibre for telecommunication cables and systems.
Our British patent application No. 8323692 describes and claims an optical fibre pulling tower constructed of a synthetic epoxy granite. We have found that this provides a resonant-free structure which is the key to manufacturing high quality fault-free fibre at high speed. This patent specification also shows how the fibre diameter is measured by a diameter measuring device and the capstan draw-off rate is dependent upon this and the preform feed rate to maintain constant fibre diameter.
However the preform is normally not of constant diameter, however hard one has tried to make it so. There are small variations in diameter and as the preform is fed into the furnace these variations in diameter can affect the resultant diameter of the pulled fibre.
We have found the conditions inside the furnace are critical to pulling a high quality low-loss fibre; in particular the flow rate of glass through the furnace at a predetermined furnace temperature and a predetermined fibre diameter must remain within close limits.
It is an object of the present invention to provide an improved arrangement for maintaining precise control of the optical fibre being drawn.